Project Summary This resubmission of application R01DA050470 proposes to use innovative approaches to identify ?hotspots,? defined as geographic areas in which high rates of HIV or HCV infection, high HIV viral loads, or drug-resistant HIV strains are found. We propose two novel approaches for identifying hotspots: 1) Use of web-based mapping technology to document observed and self-reported HIV and overdose risk behaviors among PWID in private and semi-public injection settings (SPIS) and the attributes of these risk settings; 2) Systematically collect cookers (containers used to mix and heat drugs before injecting) from injection settings and test them for HIV and HCV antibodies (testing cookers is a novel method developed in the Johns Hopkins Virology lab). We will recruit 600 HIV positive and negative people who inject drugs (PWID). These PWID will complete a survey using a software program developed by our team to locate and map the areas where they inject and attributes of these injection settings. These data will be used to identify high-risk behaviors in SPIS within census block groups (CBGs). These participants will be followed for 2 years. The findings from this observational portion of the study will then be used to inform an innovative pilot of an injection setting targeted peer-driven intervention to reduce HIV/HCV transmission and overdose risk behaviors. From the identified CBGs, we will select 60 non-contiguous CBGs for a pilot cluster randomized trial (CRT) of the intervention. The CBGs will be randomized to one of 4 conditions: 1) Peer education and stocking of SPIS with risk reduction materials, 2) Peer education only, 3) Stocking SPIS with risk reduction materials only, and 4) The standard of care. Based on their CBG and SPIS use, 120 index PWID participants will be selected from the 600 PWID. These index participants will receive training corresponding to the assigned condition of their CBG. The indexes will implement the intervention targeting two specific SPIS. Each index will also recruit PWID from their CBG to serve as data collectors. In the SPIS, the data collectors will use Ecological Momentary Assessment (EMA) and collect cookers for HIV/HCV testing. Data from the indexes (N=120) and data collectors (N=120) will be used as outcomes of the 4-arm intervention.